It depends on your use-case.
A couple of downsides of small and medium drones when your ship is far away is that NPCs are more likely to focus your drones instead of coming towards you.
And recalling the drones (or launching them) is going to take a lot of time if your ship is 80+km away from the targets.
Sentries can do that instantly.
I still think Sentry drones are pretty niche, but they can be useful in that niche.